Field
This disclosure is generally related to an electroplating apparatus used for fabrication of solar modules. More specifically, this disclosure is related to an electroplating apparatus that has an improved throughput.
Related Art
Conventional solar cells often rely on Ag grid on the light-facing side to collect light generated current. To form the Ag grid, conventional methods involve printing Ag paste (which often includes Ag particle, organic binder, and glass frit) onto the wafers and then firing the Ag paste at a temperature between 700° C. and 800° C. The high-temperature firing of the Ag paste ensures good contact between Ag and Si, and lowers the resistivity of the Ag lines. The resistivity of the fired Ag paste is typically between 5×10−6 and 8×10−6 ohm-cm, which is much higher than the resistivity of bulk silver.
In addition to the high series resistance, the electrode grid obtained by screen-printing Ag paste also has other disadvantages, including higher material cost, wider line width, and limited line height. As the price of silver rises, the material cost of the silver electrode has exceeded half of the processing cost for manufacturing solar cells. With the state-of-the-art printing technology, the Ag lines typically have a line width between 100 and 120 microns, and it is difficult to reduce the line width further. Although inkjet printing can result in narrower lines, inkjet printing suffers other problems, such as low productivity. The height of the Ag lines is also limited by the printing method. One print can produce Ag lines with a height that is less than 25 microns. Although multiple printing can produce lines with increased height, it also increases line width, which is undesirable for high-efficiency solar cells. Similarly, electroplating of Ag or Cu onto the printed Ag lines can increase line height at the expense of increased line width. In addition, the resistance of such Ag lines is still too high to meet the requirement of high-efficiency solar cells.
Another solution is to electroplate a metal grid, which can include one or more metal layers, directly on the Si emitter or on a TCO layer above the emitter. The electroplated metal grid tend to have lower resistance (the resistivity of plated Cu is typically between 2×10−6 and 3×10−6 ohm-cm) than the printed metal grid. In large-scale solar cell fabrications, throughput can be a key to reduce to the overall fabrication cost.